Imaging integrated circuits using a single-point single-photon detector and a scanning system and calculating of a per-pixel value

ABSTRACT

A Scanning Time-Resolved Emission (S-TRE) microscope or system includes an optical system configured to collect light from emissions of light generated by a device under test (DUT). A scanning system is configured to permit the emissions of light to be collected from positions across the DUT in accordance with a scan pattern. A timing photodetector is configured to detect a single photon or photons of the emissions of light from the particular positions across the DUT such that the emissions of light are correlated to the positions to create a time-dependent map of the emissions of light across the DUT. The scanning system is configured to updated the time-dependent map of the emissions based on a transformation of an underlying time-resolved waveform at certain intervals and corresponding to at least one location and generating a pseudo image of the DUT.

BACKGROUND

The present invention relates to imaging technology and moreparticularly to systems and methods for scanning integrated circuitsusing single-point single photon detector and imaging the integratedcircuits using a per-pixel value.

Hot-carrier photon emission from very large scale integration (VLSI)circuits has been employed for localizing and identifying failures incircuits. With the introduction of Emission Microscopy, hot-carrierphoton emission soon became an essential instrument for physical failureanalysis by localizing hot-spot emission, shorts, non-uniformquiescence/stand-by current of the chip (IDDQ), etc. More advancedextensions have also been added to this technique in recent years,based, for example, on the detection of the Light Emission due toOff-State Leakage Current (LEOSLC): circuit logic states mapping, powergrid drop calculation, circuit internal temperature and gateself-heating measurements, etc.

In 1995, the concept of Picosecond Imaging for Circuit Analysis (PICA),also called Time-Resolved Emission (TRE), was introduced and used. Thistechnique permits the observation in time of the faint near-infrared(NIR) light pulses emitted by hot carriers during the switchingtransitions of complementary metal oxide semiconductor (CMOS)transistors. From the optical waveforms, it is possible to extractpropagation delays, signal skews and other timing problems in anon-invasive and very effective way. These features dictated theimmediate widespread adoption of PICA by the testing and diagnosticcommunity. Emissions can be measured in a static way (integrated intime) or dynamically (timing waveforms).

The continuous trend of the modern semiconductor industry towardssmaller devices and lower supply voltages is causing significant changesin the intensity and spectrum shift of the light emitted by present CMOSgeneration. In particular, the progressive shift of the spectraldistribution of emitted light towards longer wavelengths pushed for thedevelopment of innovative photodetectors.

Although promising, all prototypes of new imaging photodetectors so fardeveloped have significant disadvantages (such as high noise, hot-spots,non-uniformity, high time jitter) that precluded their adoption for PICAmeasurements. In fact, manufacturing even single pixel photodetectorswith low noise and low jitter is complicated and leads to a very lowyield, and high cost. The manufacturing technology does not seem matureenough to yield arrays of such photodetectors to create a performingimaging photodetector.

BRIEF SUMMARY

The evolution and improvement of PICA capabilities may be influenced bydifferent photodetectors adapted to measure the arrival time of thephotons compared to a reference signal (trigger). Some detectors likethe MEPSICRON S-25™ photo-multiplier tube (PMT) may be employed becauseof their capability of measuring the spatial coordinates of the positionat which the photon arrives in addition to the instant in time. Thispermits the creation of images in time (movies) of the evolution of thelight of the chip, thus simplifying the interpretation of data.

However, the low sensitivity of such photodetectors in the Near-Infrared(NIR) region of the emission spectrum mostly limited the technique tothe observation of light pulses coming from field effect transistors(FETs) in older technology nodes or elevated supply voltage. Moreover,the emission from the p-type FET (p-FET) is more than one order ofmagnitude weaker than n-type FETS (n-FETs) and shifted towards longerwavelengths, i.e., lower photon energy. As a consequence, the delay andskews can be calculated only between logic gates having the same signalphase, and in particular in correspondence to the falling edge of thelogic gate output, when the strongest emission from n-FETs occurs.

Two photodetectors that demonstrate significantly better QuantumEfficiency (QE) in the NIR region of the spectrum, lower noise and lowertime jitter are the Superconducting Single Photon Detector (SSPD) andthe InGaAs Single Photon Avalanche Diode (SPAD). Although all thesephotodetectors offer only single-point detection capability as opposedto the imaging capability of the S-25 PMT, they permit a significantreduction of the acquisition time for the light pulses produced byn-FETs (e.g., a reduction of more than 1,000,000 times). Moreover thephotodetectors permit the observation of the light pulses emitted by theweaker p-FETs (corresponding to the rising edge of a logic gate outputsignal). This simplifies and extends the capabilities of PicosecondImage for Circuit Analysis (PICA) techniques allowing the evaluation ofsignal pulse width, duty cycle, as well as the delay and skews betweensignals with different phases.

The loss of imaging capability is a significant limiting factor forvarious reasons. In particular, time resolved imaging of the emissionpermits measurement of several transistors or gates at the same timeduring a single acquisition, eases the interpretation of the datacollected, allows the experienced user to pinpoint areas of interest forthe measurements, permits failures in unexpected areas to be visible inan image, simplifies the development of test patterns and greatlysimplifies alignment to the layout. For all these reasons, significanteffort is devoted to develop new imaging and timing photodetectors withimproved NIR sensitivity: e.g., InGaAs photo-cathodes or arrays ofsingle pixel photodetectors are needed.

In accordance with present embodiments, a method of generating a pseudoimage of a device under test (DUT) comprises receiving a plurality oflocations of interest corresponding to locations on the DUT, applying avoltage to the DUT, generating a time-resolved waveform corresponding toeach the location of interest, determining a frequency domaintransformation of the time-resolved waveforms, analyzing the frequencydomain transformations at certain intervals to determine a value foreach of the locations of interest using a respective one of thetime-resolved waveforms, and generating the pseudo image comprisingpixels, wherein each pixel of the pseudo image has the value of arespective one of the locations of interest.

According to one embodiment, a method of generating a pseudo image of adevice under test (DUT) comprises receiving a plurality of locations ofinterest corresponding to locations on the DUT, applying a voltage tothe DUT, generating a time-resolved waveform corresponding to each thelocation of interest, determining a time domain representation of thetime-resolved waveforms, analyzing the time domain representations atcertain intervals to determine a value for each of the locations ofinterest using a respective one of the time-resolved waveforms, andgenerating the pseudo image comprising pixels, wherein each pixel of thepseudo image has the value of a respective one of the locations ofinterest.

As used herein, “facilitating” an action includes performing the action,making the action easier, helping to carry the action out, or causingthe action to be performed. Thus, by way of example and not limitation,instructions executing on one processor might facilitate an actioncarried out by instructions executing on a remote processor, by sendingappropriate data or commands to cause or aid the action to be performed.For the avoidance of doubt, where an actor facilitates an action byother than performing the action, the action is nevertheless performedby some entity or combination of entities.

One or more embodiments of the invention or elements thereof can beimplemented in the form of a computer program product including acomputer readable storage medium with computer usable program code forperforming the method steps indicated. Furthermore, one or moreembodiments of the invention or elements thereof can be implemented inthe form of a system (or apparatus) including a memory, and at least oneprocessor that is coupled to the memory and operative to performexemplary method steps. Yet further, in another aspect, one or moreembodiments of the invention or elements thereof can be implemented inthe form of means for carrying out one or more of the method stepsdescribed herein; the means can include (i) hardware module(s), (ii)software module(s) stored in a computer readable storage medium (ormultiple such media) and implemented on a hardware processor, or (iii) acombination of (i) and (ii); any of (i)-(iii) implement the specifictechniques set forth herein.

Techniques of the present invention can provide substantial beneficialtechnical effects. For example, one or more embodiments may provide for:

generating a pseudo image of a device under test (DUT) at a timeinterval corresponding to an activation of an element of the DUT.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of illustrativeembodiments thereof, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the present invention will be described belowin more detail, with reference to the accompanying drawings:

FIG. 1 is a schematic diagram of a Scanning Time-Resolved Emission(S-TRE) measurement system in accordance with one embodiment;

FIG. 2 is a schematic example showing the scanning of a surface of theDUT for collecting light emission;

FIG. 3 is a flow diagram showing an illustrative method for ScanningTime-Resolved Emission microscope (S-TRE) emission measurements;

FIG. 4 is a flow diagram showing an illustrative method for generating apseudo 2D image according to some embodiments;

FIG. 5 is a flow diagram of a method for spectral analysis in accordancewith one embodiment;

FIG. 6 is an illustrative pseudo 2D image generated in accordance withFIG. 5;

FIG. 7 is a flow diagram of a method of combining waveforms associatedwith different locations generated during spectral analysis inaccordance with one embodiment;

FIG. 8 is an illustration of the method of FIG. 7 in accordance with oneembodiment;

FIG. 9 is a time-resolved waveform generated in accordance with oneembodiment;

FIG. 10 is a pseudo 2D image acquired by a scanning SSPD and using atransformation/analysis in accordance with one embodiment;

FIG. 11 is an illustration of a method of acquiring a pseudo 2D image bya scanning SSPD and using a transformation/analysis in accordance withone embodiment;

FIG. 12 is a flow diagram of a method of acquiring a pseudo 2D image inaccordance with some embodiments;

FIG. 13 is a pseudo 2D image acquired by switching of elements of a DUTin accordance with one embodiment;

FIG. 14 is a flow diagram of a continuous scan method in accordance withone embodiment;

FIG. 15 depicts an exemplary scan strategy in accordance with oneembodiment;

FIG. 16 depicts an exemplary scan strategy in accordance with oneembodiment;

FIG. 17 depicts an exemplary scan strategy in accordance with oneembodiment; and

FIG. 18 depicts an exemplary scan strategy in accordance with oneembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with present principles, methods and systems are presentedto regain imaging capability for Picosecond Imaging for Circuit Analysis(PICA) while using high-performance highly-optimized single pixelphotodetectors. Instead of developing a photodetector with imagingcapability but compromised performance, the focus is shifted to the useof single pixel photodetectors in a different optical system. Thispermits for the photodetector manufacturers to fully exploit thecapability of their technology to maximize the single pixel performance,leaving the task of imaging to the optical system.

A single pixel or single point detector is a photodetector which isunable to spatially separate a photon inside the Field of View (FoV) orcollection area. All the photons collected from a certain area/volumeare spatially associated with a point.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially a Confocal Laser Scanning Microscope(C-LSM) works by scanning a laser beam on a surface of a device undertest (DUT) and measures reflected light intensity from different areasof a circuit formed on DUT. The intensity of the reflected light ismeasured using a photodetector, which may include a PIN diode, avalanchephotodiode (APD) or photo-multiplier tube (PMT). An intensity map may begenerated using electronics which receives position information from ascanning device (x, y coordinates), and maps intensity versus positionto create an image that can be used for navigation and inspection of thedevice under test (DUT). The map represents a physical map of thesurface and its features, and is not employed in any way to measurecircuit performance or perform circuit analysis.

It is to be understood that mirrors (e.g., dichroic), optics (e.g.,lenses) and pin holes may be configured to direct light from a lasersource to the DUT and from the DUT to the photodetector to map physicalattributes of the DUT.

Referring to FIG. 1, in accordance with present principles, a scanningsystem 40 is employed for acquiring spontaneous light emission (not thelaser reflections) from different areas of a DUT 14 and focuses thephotons onto a timing photodetector 42 (e.g., SPAD, SSPD, PMT, etc.)that is capable of precisely measuring the arrival time of single-photonon a picosecond time-scale. This may be referred to as a ScanningTime-Resolved Emission (S-TRE) measurement system 40 with enhancedcapabilities for enabling PICA for modern and future semiconductortechnologies. It should be understood that there may be applicationswhere excited emissions may be measured in addition to or instead of thespontaneous emissions. System 40 permits imaging capability for PICA byusing a high-performance single point/pixel photodetector 42, amongother things.

Time-Correlated Single-Photon Counting (TCSPC) electronics 44 associatedwith the optical system 40 receives a photon arrival signal 56 from thephotodetector 42, a trigger signal 46 (reference signal) from the DUT 14or a timing generator (not shown), and the actual XY (51) (and Z (53))position from a scanner 20 at the time of the photon detection. Adatabase 52 stores the delay between the photon arrival time and thetrigger signal, along with the pixel coordinates in the image.

In one embodiment, the S-TRE system 40 includes an optical system 54 tocollect light from a DUT and focus it onto a photodetector 42. Theoptical system 54 may include one or more lenses 28, pinholes 30 andmirrors (not shown), as needed. A scanning system 20 permits movementover the collection area across the DUT 14 to collect spontaneousemissions and mark their location of origin. A timing photodetector 42detects the spontaneous or other emissions. Photodetectors 42 mayinclude a photo-multiplier tube (PMT), Superconducting Single PhotonDetector (SSPD), InGaAs Single Photon Avalanche Diode (SPAD), or othertype and preferably include high time resolution, low jitter, low noise,and sufficiently high count rate and signal dynamics.

Characteristics of the photodetector that are highly desirableinclude: 1. high sensitivity in the wavelength range of the circuitemission (1.0 microns-1.5 microns); 2. high time resolution (low jitter)in detecting the arrival time of the photon compared to a referencetriggering signal (few tens of picoseconds, e.g., better (lower) thanabout 40 ps to 50 ps); 3. low noise (low dark count rate, or falsecounts not due to photon detections); 4. large signal dynamics (i.e.,high count rate capability).

A triggering mechanism 58 from the DUT 14 or external timing generatorgenerates a trigger signal 46 to activate a TCSPC system 44. The triggersignal 46 provides a synchronization mechanism with current operationsof the DUT 14 and indicates an instant when an event occurs on the DUT.The TCSPC system 44 receives several inputs. For example, at least aphoton arrival signal 56, the trigger input 46, XY scanner position 51from scanner 20, (and possibly a Z position 53 of the system from amicroscope or optical system 54). A database of “events” 52 records thespontaneous emissions detected and the corresponding position from whichthe emission was detected. The database record may include at least oneof the time delay between the photon arrival time (56) and triggersignal (46), and an XY position 51 of the scanner 20 at the time ofevent. A Z position 53 may also be recorded along the instant in timefrom the beginning of the measurement.

Operations of system 40 are preferably monitored and controlled using acomputer system 57. Computer system 57 is configured with hardwareand/or software to provide control signals 55 to control and synchronizeoperations of, e.g., the scanner 20, optics system 54, photodetector 42,electronics 44, storage in database 52 and/or trigger signal generation.System 57 may also include software for employing the data collectedfrom the DUT 14. The DUT 14 is preferably a powered semiconductor deviceor circuit. Other DUTs may also be employed. However, the DUT preferablyproduces emissions on its own by virtue of on-chip events andoperations.

A user can interact with computer system 57 using an interface 59 to gettime-integrated images, timing waveforms, manipulate the data andanalyze the circuit of the DUT 14. The interface 59 may include agraphical user interface and system input devices (e.g., mouse,keyboard, etc.).

Event records in a measurement set can be stored in database. Eachrecord may include an event index field. An event time field stores theevent time from the beginning of the measurement or time of day (lowtime precision). A time delay field includes a time delay (t_(ph)) of aphoton arrival time from the trigger signal. This is a high precisiontime reference. A position of scanner 20 (X,Y) and optics (Z) at thetime the photon is detected may be stored in a position field(s). Notethat the data stored may be in any suitable format.

Scan speed and pattern can be adjusted to optimize the collection of theemission from different types of devices under test. Furthermore, thespeed and pattern could be adjusted dynamically during the S-TREmeasurement based on previously acquired data. For example, by spendingmore time on regions of low emission (to enhance the signal to noiseratio), or to avoid spending time on regions where there is no emission,etc. This step may be done automatically with prefixed algorithms storedin computer system 57 (FIG. 1) or by user intervention during themeasurement. The user may notice regions of particular interest thatneed more attention and use more time scanning these areas. In addition,with knowledge of the types and functions of the devices on the DUT 14,a most likely or preferable pattern may be selected (at least initially)based upon historic information or statistics regarding that type ofdesign or structure.

The scanning of the DUT 14 could be performed either in sync or out ofsynch (asynchronous) with the trigger signal 46, depending of theapplication and situation. Compared to a simple mechanical stagetranslation of the DUT 14 under a conventional microscope, the systemsand methods in accordance with the present principles permit for abetter rejection of mechanical vibrations and drift. In particular, theresonant oscillation movement of the scanner permits achieving a betterrepeatability of the acquisition position.

For example, with the present techniques, emission image frames areacquired from an entire region of interest of the DUT 14 in a “short”frame time as compared to the total acquisition time. Many frames arethen acquired to account for the entire acquisition time. If from oneframe to the next, the DUT has mechanically drifted, mathematicalmethods implemented in e.g., software on system 57 may be used tocorrect for the drift. This is difficult when using a stage scanning theDUT 14, because the drift information cannot be extracted since thedrift information affects each pixel differently. Another problemrelated with the creation of images based on stage movement is due tothe recent widespread use of Solid Immersion Lens (SIL) optics in modernPICA tools to enhance the collection efficiency and the navigation imagequality. The SIL requires direct contact with the sample and thereforethe movement from one acquisition point to the next is achieved by“hopping”, which unfortunately does not provide good repeatability ofthe detector positioning.

The photon database 52 may be processed in a way to createtime-integrated images of the emission from the DUT 14 using “partial”data at different stages of the acquisition (frames). The comparison ofthese images permits the observation of mechanical drifts or movement ofthe DUT 14. The drift can be measured, and the database 52 is processedto correct for the drifts. This could be done at the end of themeasurement (post-processing) or during the measurement (real-time).

One aspect of the present embodiments includes using a scanning system20 (such as the scanning capability of the C-LSM) to create an image ofthe emission collected from the DUT 14 by using a single pixelphotodetector. If the Scanning Time-Resolved Emission (S-TRE) system 40is implemented in a C-LSM, the LSM low speed photodetector may bereplaced with or switched out in favor of a timing photodetector 42 thatis capable of precisely measuring the arrival time of single-photon withpicosecond precision.

Scanning Time-Resolved Emission microscopes (S-TRE) (microscopes/systems40) are shown in accordance with illustrative embodiments. Thesingle-photon detectors may be used in a counting/integrating modeduring navigation mode. In this mode, during the PICA measurements, thelaser source is turned off while the XY scanner 20 is used to directlight emitted from different areas of the DUT 14 onto the single-photondetector 42. This permits the removing of imaging requirements from thephotodetector thus allowing the optimization of the performance of thesingle-pixel detector for very high detection efficiency, low dark countrate (noise), and high time resolution.

Compared to a single point acquisition, this scanning technique has thedisadvantage of causing an increase in the total image acquisition time,which is roughly linearly proportional to the number of pixels. Such adisadvantage may often be acceptable given the elevated sensitivity ofpresent single-pixel detector and the long list of previously mentionedadvantages of imaging capability. The XY scanning range can also beadapted to cover different areas of the circuit and change the number ofcollected pixels.

Referring to FIG. 2 with continued reference to FIG. 1, a scanningprocedure is illustratively shown to collect the spontaneous lightemission from a DUT 14. When the scanning system 20 is activated, lightemission from different portions of the DUT 14 can be collected,depending on the position of the XY scanner 20. Assume that the scanner20 is in position (1,1) for a time T11. If a photon is detected in thistime window by the timing photodetector 42, the TCSPC electronics 44will measure its time separation t.sub.ph compared to the trigger signal46 and create a database entry 60 to record with the calculatedt.sub.ph, the XY location (1,1) and possibly the z position of theoptics as well as the time from the beginning of the measurement.Independently from the fact that zero, one or more photons have beendetected, after the time T11, the scanner 20 will move to a nextposition, say (1,2) and wait there for a time T12 (that may or may notbe the same as T11). Again, if photons are detected in this position,they will be labeled (1,2) in the database 52. The scanner 20 movesalong all the positions of the DUT 14 and then repeats the cycle orpattern 82 from (1,1). The positions may be changed during theacquisition, some of the pixels may be ignored or the time spent on thepixel may depend on previous acquired data. In other words, the patterns82 can be modified depending on historical data, knowledge of the DUTdesign, or other criteria.

The TCSPC electronics 44 receives a photon signal 56 from thephotodetector 42, a trigger signal 46 from the DUT 14 or from the timinggenerator 72, and the actual XY position from the scanner 20. Eachphoton is therefore associated with its time delay from the triggeralong with the pixel in the image. A multi-channel analyzer or PC 57 canthen be used to plot the data in many different ways, among them, forexample: (1) movies; (2) time-integrated images of the emission, inwhich only the information associated with the spatial coordinates ofthe photon is used while the arrival time is neglected; (3) timingwaveforms of portions of the acquired image; (4) different types ofpixel integration and selection based on the DUT layout; and (5) anyother display format or image.

For each pixel, a timing waveform of the emission can be constructed byselecting only the database records with the specified XY location andcreating a histogram of the arrival time of the photons compared to thetrigger. Different pixels can also be associated and their data mergedto improve the signal-to-noise ratio, by reducing the spatialresolution. In addition, if the timing information of the databaserecords is ignored, a time-integrated image (frame) of the emission canbe constructed, for example using the intensity of each pixel of theimage corresponding to the number of photons detected with the scannerin that position. Creating many different frames, corresponding todifferent successive time windows in the acquired data, can then be usedto generate a movie.

Assuming that, if averaged over a long time period, the emission fromthe DUT does not change, time-integrated images extracted at differentmoments in time during a long acquisition time should look the same(with the exception of noise in the images). Therefore, this comparisoncan be used to detect mechanical drift of the system, calculate theamount of drift and correct for the drift by modifying the XY locationof the photons detected after the drift has taken place.

The system in accordance with present principles is compatible withcooling technologies (e.g., spray, air, diamond window) as well as Solidand Liquid Immersion Lenses to enhance the optical Numerical Aperture ofthe microscope and therefore reduce the acquisition time. Adaptivealgorithms could also be used to give higher exposure time to some ofthe pixels of the images depending on the previously acquired photonsduring the same acquisition, thus permitting a possible reduction of theacquisition time. The scan area could also be changed during theacquisition through user intervention.

Referring to FIG. 3, a method for Picosecond Imaging for CircuitAnalysis (PICA) using a Scanning Time-Resolved Emission (S-TRE)microscope is illustratively shown. In block 120, an experiment ormeasurement is set up. This includes setting up a device under test(DUT). In block 122, the DUT is navigated (e.g., using a navigation modeor navigation capability of a system) to select an acquisition position.The navigation may be set up using for example, a scanning device of aC-LSM. In block 124, if present, a laser source (for navigation, etc.)is turned off and a timing detector is enabled to perform emissionsmeasurements.

In block 126, a scanning pattern is set up. The pattern may be adjustedor customized based on statistical information, the DUT design,historical data and/or any other information. The scan pattern mayinclude parameters such as the area to be scanned, number of pixels,time per pixel, etc. In block 128, an initial acquisition is begun. Thisis followed by scanning to a new location. Trigger signal generation isalso provided.

In block 130, acquisition at a particular location is conducted. Inblock 132, a determination is made of whether a photon from spontaneousor other light emissions from the DUT is detected using a timingphotodetector capable of single photon detection, preferably a singlephoton, single point photodetector. If no photon is detected, the pathcontinues the acquisition step until the predetermined acquisition timeis exceeded.

If a photon is detected, in block 134, the photon arrival time iscompared with the trigger signal to compute delay. In block 136, scannerposition and the photon arrival time are correlated. In block 138, theposition, and times for the photon are stored in a database.

The following steps may be performed after a single acquisition, groupof acquisitions or as post-processing. In block 140, the data collectedfor the photon is analyzed or employed to be displayed in e.g., anintensity map, movie, etc. In block 142, mechanical drift is evaluatedby a user or using software. If mechanical drift is determined, thephoton positions are corrected for the drift in block 144. In anotherembodiment, the mechanical drift is evaluated during the measurement andnot at the end. Otherwise, a determination of whether the acquisitionprocedure is complete at the present location is made in block 146. Thisdetermination may be made by the user, software or other criteria.

If the acquisition is finished, a PICA or other analysis of the photondata may be made. This may include circuit analysis on integratedcircuits or other devices or samples having spontaneous or intrinsiclight emissions. Otherwise, the path returns to block 130 foracquisition at a next location.

In one embodiment, an S-TRE is provided in combination with a LaserScanning Microscope, and the method further includes directing emissionstoward the timing photodetector using a moveable mirror or other device.The moveable mirror is moved out of the optical path during a navigationmode when the scanning system of the laser scanning microscope defines aposition. Then the moveable mirror is moved into the optical path tocollect and redirect spontaneous or other emissions (laser is off) tothe timing photodetector.

According to one embodiment and referring to FIG. 4, a pattern image(with or without a scanner) is acquired for an initial acquisitionposition (xs,ys) (e.g., by moving the stage) in block 401, revealingfeatures within a FOV in block 402, which is divided into N×M pixels,and enables a determination of a list of locations of interest (xi,yi)in block 403.

In one embodiment, a method of creating a pseudo 2D image is depicted inconnection with blocks 403-410, wherein the list of scan locations(xi,yi) is determined in block 403, and for each of the locations ofinterest (xi,yi) in block 404, the method acquires a time-resolvedphoton(s) in block 405, analyzes the time-resolved photon(s) (optionallycreating a time-resolved waveform) in block 406, determines a Figure ofMerit (FOM) (e.g., within a time- or frequency-domain) in block 407,determines the intensity/color of a pixel (xi,yi) or a pseudo 2D imagebased on a previous FOM in block 408 and determines whether theacquisition procedure (e.g., blocks 404-409) is complete at the presentlocation in block 409.

According to some embodiments, a pseudo 2D image is output at block 410.According to one embodiments, time-resolved waveforms are updated atblock 411.

Embodiments of the present application will be described in the contextof FIG. 4, illustrating an exemplary method of creating time-resolvedemission images of integrated circuits using a single-pointsingle-photon detector and a scanning system.

According to one or more embodiments, and referring to block 411 of FIG.4, enhanced TRE waveforms are generated using pseudo 2D images generatedby the system 57 (see for example, image 600, FIG. 6). In oneembodiment, the computer system 57 and user interface 59 are configuredfor generating improved pseudo 2D PICA images by computing a per-pixelFigure of Merit (FOM) and improving a SNR of the TRE waveform.Conventional systems can be slow to resolve an image of a pixel.According to one embodiment, pico-second image resolution (per pixel)can be achieved.

Given a data set corresponding to a pseudo 2D image and a pseudo 2Dimage created to represent a feature of interest for the measurement,one embodiment of the present invention includes constructing one ormore TRE waveforms using photons corresponding to a list of (x,y) pixellocations designed to maximize the SNR of the waveform or portion of thewaveform. Pixels of the 2D image are added to, or removed from, the listbased on their positive or negative contribution to the SNR of thewaveform.

Given a data set corresponding to a pseudo 2D image and a pseudo 2Dimage created to represent a feature of interest for the measurement,one embodiment of the present invention includes constructing one ormore TRE waveforms using photons corresponding to a list of (x,y) pixellocations in the FOV that correspond to circuit locations and featuresthat produce nominally identical or equivalent signals. For example,multiple identical buffers in parallel. In practical circuit designapplications, a larger buffer may be broken in multiple smaller buffersin parallel to reduce self-heating.

Referring to FIG. 5, in a method 500, the system 57 obtains a list ofscan locations 501, and for an initial location (e.g., x1,y1), a firstTRE waveform W1 is acquired using the photons detected at scannercoordinates (x1,y1) 502. For each subsequent location (xi,yi) in thelist, construct a new waveform W2 by combining the photons detected atscanner location (xi,yi) and those included in W1 (i.e., (x1,y1) in afirst iteration) 404. If the system 57 determines that the SNR of W1 isbetter than W2 505, then the method advances to a next location in thelist (503) discarding W2. If the computer system determines that the SNRof W1 is not better than W2 505, then the method updates W1 to includeall of the photons corresponding to W1 and W2 and advances to a nextlocation in the list (503). As a result, after the first iteration, thenew best waveform W1 may include the photons at location (x1,y1) and(x2,y2) combined.

In view of the foregoing, at block 505, the SNR of W1 and W2 (the entirewaveforms or a portion of the waveforms) are compared. In oneembodiment, at block 505, if the SNR of W1 is higher than SNR of W2,then the waveform W1 is maintained, the photons detected at thecoordinate corresponding to W2 are not included in waveform W1, and anext location in the list is used to construct a new W2 at blocks503-504. Again, at block 505, if the SNR of W1 is lower than the SNR ofW2, then “W1=W2” such that W1 is updated to include all of the photonscorresponding to W1 and W2 at block 506, and a next location in the listis used to construct a new W2 at blocks 503-504.

According to one or more embodiments of the present invention, an imageof the electronic device is generated or updated 507 using the firstwaveform updated to be equal to the second waveform.

According to one or more embodiments of the present invention, themethod 500 of FIG. 5 ends when there are no more locations to consideror the SNR does not grow anymore. In one embodiment, the number ofiterations depends on the length of the list of scan locations 501. Ingeneral, the number could be small, including a pixel of interest 1601and the surrounding adjacent pixels, e.g., 1602, as illustrated in FIG.16.

According to one embodiment, it should be understood that the method 500is re-initialized when a new S-TRE image is acquired/analyzed or if anew location of the existing image is being analyzed. Further, it shouldbe understood that the list of locations can be using a variety ofmethods, for example, as illustrated in FIG. 15 or FIG. 16. One ofordinary skill in the art would understand that the list can begenerated using different methods, and that the present disclosure isnot limited to exemplary embodiments described herein.

It should be understood that according to one or more embodiments of thepresent invention, the method 500 can be repeated with differentpermutations of the list of scan locations.

Referring to FIG. 5, according to one embodiment of the presentinvention, a first W1 waveform is constructed using the photons detectedat pixel 1. A second waveform W2 is constructed using the photons atlocation 1 and 2. The SNR of the waveforms W1 and W2 is compared and W2is determined to be less than W1, so that location 2 is not included inthe final waveform (i.e., W1 is maintained). A new waveform W2 isconstructed using photons at location 1 and 3. The SNR of W1 and W2 arecompared and W2 is determined to be greater than W1. According to themethod 500 of FIG. 5, and block 506, “W1=W2” so that it includes all thephotons detected at locations 1 and 3. A new waveform W2 is constructedusing photons at location 1, 3, and 4. The SNR of W1 and W2 are comparedand W2 is determined to be greater than W1. Then “W1=W2” so that itincludes all the photons detected at locations 1, 3, and 4. At the endof the process 500, W1 is the best waveform and is returned to the userand/or for additional analysis.

According to one embodiment, the new W2 waveforms can be constructed byadding the waveform at the new location (xi,yi) to be evaluated to theexisting W1 waveform, since the method is linear.

Referring to FIG. 7, according to one embodiment, a method 700 ofconstructing a TRE waveform includes analyzing the layout/schematic todetermine if there are multiple locations that generate identicalsignals 701, mapping the layout locations onto the pseudo 2D imageacquired with the system 57 at block 702, and combining the photons atthose locations to create a new waveform at block 703. According to oneor more embodiments of the present invention, an image of the electronicdevice is generated or updated 704 using the waveforms updated for eachlocation of interest. For example, as illustrated in FIG. 8, fourlocations (1, 2, 3, 4) of equivalent buffers are located onto the pseudo2D image 808 and their emission signals are combined to create a newwaveform 802 with a higher SNR.

According to one or more embodiments, and referring to block 407 of FIG.4, the pseudo 2D images generated by the system 57 are improved bycomputing a per-pixel FOM, wherein the pseudo 2D image intensity/coloris generated from a transformation/analysis applied to the photodatabase 52 using, for example, a frequency domain analysis (such asFast Fourier Transform, FFT) of the time-resolved waveforms generatedusing the photons in each pixel, a time-domain windowing of the photonsassociated with each pixels, or a time-domain correlation of thetime-resolved waveforms generated with the photons collected in eachpixels.

According to one embodiment, the frequency-domain includes any analysisof the time-resolved emission of a location after the time informationhas been transformed into a frequency or wavelength domain using, FFT oranother transformation. According to one embodiment, time-domainanalysis includes any analysis performed on the time resolved waveformsthat are directly constructed from the time resolved photos measured ina pixel.

According to one embodiment, hardware 48 including, for example, aspectrum analyzer, oscilloscope, network analyzer, or other hardwaresignal analysis system such a Digital Signal processor (DSP) is added tothe system in FIG. 1 to process the photon database 52 and create apseudo 2D image 59. As an alternative, the proposed method can beimplemented as a software program running on the system 57 described inFIG. 1 and implemented at block 140 of FIG. 3.

It should be noted that although other possible analysis/transformationmethods may be developed, the intensity/color of any pixel of the pseudo2D image may not be a direct/proportional function of the number ofphotons that have been detected and associated to a given (x,y) locationof the scanner head. Notwithstanding the foregoing, in other cases, thetransformation can be a linear function, and the transformed image maybe proportional to the intensity. According to one or more embodiment,the pixel intensity is a result of the analysis of the photons in thecorresponding pixels after a time-resolved waveform has been generatedfrom those photons and a transformation/analysis has been applied togenerate a Figure of Merit (FOM).

It should be understood that, according to one embodiment, the FOMidentifies a quantitative measure of a parameter/feature of interest,which can be compared across multiple scanned locations. For example, todetermine which location has a signal switching at 1 GHz, whenperforming the frequency domain analysis, create a FOM corresponding tothe amplitude of the spectrum at 1 GHz, which is a measure of how strongthe signal at 1 GHz is at each location. According to one embodiment, bycreating a corresponding 2D image, the locations switching at 1 GHz canbe identified. It should be understood that this is an exemplary,non-limiting FOM and that different FOM's are contemplated, for example,in which a total intensity of the spectrum is normalized, a DC componentis normalized, etc.

In accordance with some embodiments, for scanner (x,y) coordinates, thearrival time of all the photons at those coordinates are organized intoan histogram corresponding to a time-resolved waveform (e.g., see FIG.9, waveform 900). The corresponding waveform is subsequently analyzed tocalculate a FOM that is used to determine the intensity/color of thepixel of the pseudo 2D image at the corresponding (x,y) location. Forexample, FIG. 9 illustrates a time-domain analysis, such as timewindowing, for pseudo 2D images highlighting the rising/falling edge ofa transition, as well as the leakage of the gate. A emission spot ofinterest in an image can be analyzed by breaking it down in itscomponents to determine if an anomalous leakage path exists in specificlogic states or during switching events. From the same acquisition auser can also extract a measure of the gate switching activity,corresponding to rising edge 901 and falling edge 902, as well as a mapof the gate leakages to target variability and self-heatingapplications.

FIG. 10 shows an exemplary FOM calculated by first computing a frequencydomain transformation of the time resolved waveform (such as using aFFT), then the amplitude of the calculated FFT at one or more specificlocations is used to determine the value of the FOM 1000. The result isthat the 2D image clearly highlights regions/gates (e.g., 1001, 1002) ofthe DUT that are affected by the switching activity, while reducingnoise and removing gates of less (e.g., no) interest. This allows forimproved spatial resolution, better understanding of the circuit, easierregistration of the emission against layout and pattern images, etc.

Referring to conventional tools for failure analysis, which may usetime-integrated imaging detectors such as Charge Coupled Devices (CCD),InGaAs camera, MCT (MgCdTe) cameras, etc., these cameras areintrinsically capable of spatially resolving the emission (2D) that isintegrated over a user-defined period of time. These cameras are usefulbut do not provide significant insight into the dynamic behavior of theDUT due to their limited frame rate.

According to one embodiment, a pattern image of a DUT is first acquiredusing a laser illumination and the scanner head. A ROI of the DUT isselected and re-scanned by the scanner head following a raster scanning.For a given location (i.e., a location of interest), TRE is acquired bythe SSPD for a time corresponding to the predetermined dwell time of thescanner head. Depending on the type of FOM selected, a TRE waveform canbe generated using the time-tagged photos acquired at the (x,y)location. A corresponding FOM is computed and used to determine thevalue (e.g., intensity/color) of a pseudo 2D image that is output andpresented to the user. Although, this exemplary method can beimplemented live by the tool, the analysis can be implemented as apost-processing by the system 57.

FIG. 11 is an illustration of a method 1100 of acquiring a pseudo 2Dimage by a scanning SSPD 42 and using a transformation/analysis inaccordance with one embodiment. According to embodiments of the presentinvention, a tool user can identify which locations of the chip (e.g.,which transistor/gates of the circuit) are toggling, for example, at aspecific frequency, versus which region of the chip is not receiving thesignal. Such an image simplifies tasks including localizing breakpoint/fails in wires, scan chains, and other types of circuits. Such asystem is capable of visualizing locations of the DUT that are switchingat one or multiple frequencies. More specifically, the system creates atime-resolved waveform of the signal at a given (x,y) location byfiltering the photons in the database using such coordinates andconstructing an histogram of the arrival time 1101. The histogram showsa pulse delay between peaks. More particularly, histogram 1101 shows afirst peak 1103 corresponding to a supply voltage and a second peak 1104corresponding the toggling of the transistor/gate. A FOM measuring thetoggling activity is calculated and used to generate an appropriateintensity/color of the final 2D image corresponding at the (x,y)location 1102.

In one embodiment with multiple frequencies, the sum of the FFTamplitude at all such frequencies could be used to compute the FOM. Itshould also be understood that the value of the frequencies of interestmay be determined by the user based on the known DUT operation. Exampleof frequencies of interest may be the DUT clock frequency, the datafrequencies, as well as multiples, sub-multiples and combinations ofsuch frequencies. In some embodiments the phase of the FFT could be usedinstead or along with the amplitude to generate a separate pseudo 2Dimage so to have information regarding the delay. Other types offrequency domain transformations could also be used.

In alternative, to achieve similar results, time domain low pass, bandpass, or high pass filtering could be used to emulate the frequencydomain analysis with techniques commonly available for digital signalprocessing.

Referring to FIG. 12, a method 1200 of acquiring a pseudo 2D image inaccordance with some embodiments includes determining a plurality oflocations (xi,yi) (e.g., scanner coordinates) 1201, and successivelyapplying a set of (predetermined or given) voltages Vj (where Vj isindex-changing value of a power supply). More particularly, the methodincludes applying a voltage Vj to the chip by controlling a power supplylevel 1202. Each location (xi,yi) is scanned (see block 1207) for at thevoltage Vj 1203 (see block 1208), where an arrival time of photons isdetermined at the location, and a time-resolved emission is acquired1204, where a time-resolved waveform is constructed by creating anhistogram of the arrival time of the photons. A FOV is determined 1205,for example, based on the histogram showing a pulse delay between peaks,and the color/intensity of a pixel of the pseudo 2D image is determined1206 with a (xp,yp), wherein xp is determined based on (xi,yi)(e.g.,yp=yi) and yp is determined based on the voltage Vj (e.g., xp=j index).

According to one embodiment, at block 1205, the FOV can be determined bydetermining a time location of a first emission peak (e.g., 1103) and asecond emission peak (e.g., 1104) and creating a FOM based on the timeseparation between the peaks.

In view of the foregoing, according to one embodiment, at 1206, atime-domain analysis can be performed, such as measuring delay, period,amplitude at certain times, time integrate, or other time domainfilters. According to some embodiments, at 1206, an FFT could beperformed to transform the time-resolved waveform into its frequencyspectrum.

It should be understood that other quantities can be used to determine(xp and yp), as well as a different determinations of the FOM (asdiscussed herein). Furthermore, in at least one embodiment, xp or/and ypcan be related to a quantity related to the stage position (xs,ys), thescan position (xi,yi), electrical characteristics of the chip operation(e.g., supply voltage, clock frequency, initial pattern, input data,temperature), etc.

FIG. 13 presents the results of another embodiment, in this case, a FOM1300 calculated based on the time-windowed integral of the time-resolvedwaveforms of the detector, instead of using frequency domain/spectralanalysis. Referring again to the waveform example in FIG. 8, one canobserve that the emission intensity of a given location is notstationary in time but shows features, e.g., 1301-1302, that correspondto specific DUT states such as gate switching events and gate state. Theimages generated using the prior art correspond to a complete timeintegration of the photon counts across the entire measurement time,without any attention to the fact that different phenomena take place atdifferent times. According to one embodiment, a FOM is generated tocreate the 2D image based on the integral of the time resolved waveformin specifically determined intervals. In particular, by integrating thewaveforms at each (x,y) location during time intervals corresponding toexpected switching activity, an image can be generated to correspondingto specific transistors/gates activations. Once again this could help tounderstand the circuit behavior, identify failing locations, improveresolution, and simplify registration to layout and pattern images.

In one exemplary embodiment, the time interval is chosen to select timeswhen there is no switching activity and the logic state of the circuitis maintained, so that leakage emission maps could be calculated andused to determine the logic state of the gates, as well as estimate theleakage power.

In one exemplary embodiment, and referring to block 403 of FIG. 4, thevalue of the pseudo 2D images generated by the system is improved byaltering the raster scanning approach used to generate the pseudo 2Dimage intensity/color using, for example, non-uniform dwell time (e.g.,between about 1 second and several minutes) based on layout informationand/or measured signal intensity, or non-uniform stepping/rasteringduring scanning.

In one exemplary embodiment, the pixel dwell time (time spent acquiringemission at a given (x,y) pixel position) is not uniform across theentire FOV or region of interest. This is accomplished by modifying thescan control system 20 to receive an input that controls the advancementor positioning of the scan based on the current or previous measurementsfrom other/neighboring pixels, for example, at block 140 of FIG. 3. Inone embodiment, the system 57 uses an adaptive dwell time adjustmentbased on the emission signal intensity of previous or neighboring pixelsdetermined at block 140. That is, in one embodiment, block 140 includesa live analysis of emission intensity, which is used to adjust the dwelltime.

In one embodiment, the dwell time is adjusted so that the Signal toNoise Ratio (SNR) of each pixels is equalized. For example, longer dwelltimes can be allocated to pixels with lower signal intensity to increasetheir SNR. Accordingly, a total measurement time can be managed and theindividual pixels acquisition times can be adjusted accordingly. In oneembodiment, each pixel of a final pseudo 2D image is normalized based oneach pixel's dwell time.

In some practical applications, a user may want to implement amethodology where the ROI is continuously traced by the scanner headwith a determined speed. Photons would be continuously acquired andtagged with time and the (x,y) position of the scanner head.Accordingly, images are generated with progressively better SNR throughthe allocated acquisition time. This approach can give a more rapidfeedback to the user.

According to some embodiment, the scanning sequence has a per pixeldwell time sufficiently long to make a determination of the 2D image ina single pass. For this reason the pixel dwell time and totalacquisition time are related to each other by total number of pixels N*Min the image (where N and M are the vertical and horizontal size of thefinal image in pixels):total acquisition time=N*M*dwell time.

This equation does not consider the additional times that may berequired to move the probe location, start/stop an acquisition, andcompute the image. Using this approach, the user can see the imageprogressively grow as new pixel locations are added but does not have asense if the overall shaper of the emission spots until the acquisitionis completed. This is may be inconvenient if the location of the spot ofinterest is only acquired towards the end of the measurement or if theemission spot is very bright, or if the emission is acquired to decideadditional steps.

In particular, in this operation, the scanner head may be moved to aspecific probe location, an emission measurement may be started for adetermine time (dwell time), the data may be analyzed to create thecorresponding 2D image pixel intensity/color, then the scanner is movedto the next location and the process is repeated until completion.

According to one embodiment, an emission acquisition is initialized witha time corresponding to the total image acquisition time and the scannerhead is continuously moved from one location to the next, withoutstarting/stopping the emission acquisition during each step (see FIG.12). Each location is probed K times with a dwell time that is:Dwell time=total acquisition (act) time/N/M/K

One advantage of this approach is a complete 2D image is created muchfaster (in about 1/K) of the acquisition time, and is refreshedfrequently to improve its SNR (evert 1/K of the total act time). Thismay provide a sense of the emission presence/absence and its shape tothe user in a much faster way. It should be noted that the user can alsodecide to interrupt the process prematurely and start a new measurementwith a more focused target and field.

In at least one embodiment and referring to FIG. 14 depicting acontinuous scan method 1400, for a list of scan locations 1401, theimage acquisition is initialized 1402 with a small initial acquisitiontime determined for each pixel. For each scan location 1403, based onthe signal acquired 1405 using a current dwell time 1404, a decision ismade if the measurement at that (x,y) location needs to be terminated orcontinued 1406. In the case that the measurement is terminated, thescanner is moved to a next measurement location and a new measurement isstarted 1203.

In some embodiments, multiple threshold values may be used at 1405. Inother embodiments, the threshold may be based on a total intensity, atime-windowed analysis of the signal, or a spectral analysis of thesignal. In one proposed embodiment, pixels with no useful detectablesignals may be assigned a shorter dwell time so that more time could bededicated to pixels with a promising signal intensity.

According to one or more embodiments, scanning plans can be configuredto reduce an overall acquisition time. These may include creating asparse coverage of the area followed by a targeted selection ofadditional pixels as shown in FIG. 15. In this case, instead ofimplementing a raster scan of the region of interest (ROI) from a corneror the center of the ROI, a scan plan is implemented as sparse coverageof the ROI as shown by the dark pixels in the scanner mask. Locationswith low FOM (e.g., location 1—1501) may not receive additional time,while locations with elevated FOM (e.g., location 2—1502) may be furtheranalyzed by adding additional probe points as surrounding pixels, e.g.,1503.

In one exemplary embodiment, the step size of the scanner head isvariable/adjustable. In particular, instead of systematically movingbetween pixels based on time, larger steps or more complicated stepprocedures can be used. For example, an initial scan is acquired byusing a step size multiple of the minimum step size, for example, equalto two (note that different step sizes are also including different stepsizes in x and y direction). Referring to FIG. 15, one could firstacquire a signal from one of the dark locations (note that shading isused for identification in this case and is not related to the imaging)arranged, for example, in a check-board configuration 1500. This allowsfor an increase in the FOV or ROI for a given acquisition time becausethe number of measurements is reduced quadratically with the step size.The initial check-board scan is then analyzed, and based on the measuredemission intensity at a given location and/or neighboring locations,additional higher resolution scans may be started, e.g., around position2 (1502). Considering, for example, location 1 (1501) with low/nosignal, no additional data needs to be acquired around that locations.On the other hand, location 2 is found to have a promising/interestingsignal intensity. As a consequence, additional acquisitions may beacquired around that area as shown by the surrounding (four) pixels notcovered by the initial scan (e.g., location 1503).

It should be noted that a decision can be made at the end of the first(check-board) scan with all the information available or it could betaken on the flight based on the live data. In the case of using livedata, a larger step scan can continue until useful data is located, thenthe scan step is reduced for the next X pixels until the data disappearsagain and the step can be increased again. Such an adjustment can bemade at multiple points during a measurement. Additionally, it should benoted the initial scan need not follow a checker-board strategy. Forexample, the location position and step size may be driven by existinginformation such as circuit layout or pattern images of the DUT or as arandom sampling.

In another embodiment, the scanning head may first target a specificlocation 1 (1401) as shown in FIG. 16. This location may be based onpreexisting information such as circuit layout or pattern images of theDUT. A subsequent set of images may be acquired around the initial (x,y)location (e.g., at 1602) to improve the signal quality, resolution ofneighboring gates, or understanding of the acquired signal.

FIG. 16 shows one possible strategy where all the immediate surroundingpixels are acquired and included in the pseudo 2D image for analysis.Different strategies are also possible depending on the applications,and user input. For example, if horizontal spatial resolution is neededto separate two horizontally spaced gates/transistors, only horizontalcross section pixels may be added to reduce the acquisition time.Similarly, if only a vertical resolution is needed, only verticallyaligned pixels may be added to the scan procedure. It should also beunderstood, that additional pixels may be added in a third phase, fourthphase, etc., of the scan, so that the region of interest in enlarged toencompass data deemed useful by the user.

In another embodiment, the initial location “1” 1601 in FIG. 16 ismanually selected by a user or automatically determined based on acircuit layout alignment or image recognition algorithms applied to thepattern. Multiple locations can be initially determined. The system willthen proceed to point the scanner head at each of the initial locationsand acquire a small area scan at each of those as described above. Thismode would allow the user to make an initial assessment/decision andstep away from the tool during potentially long acquisitions.Additionally, this could allow automatic diagnostic methods werewaveform around area of interested and automatically acquired and arelater analyzed by the user.

In another embodiment, the shape of the scanned area would be determinedby either circuit layout information or pattern images of the DUT.

Recapitulation:

According to one or more embodiments of the present invention, a methodof generating a pseudo image of a device under test (DUT) comprisesreceiving a plurality of locations of interest corresponding tolocations on the DUT, applying a voltage to the DUT, generating atime-resolved waveform corresponding to each the location of interest,determining a frequency domain transformation of the time-resolvedwaveforms, analyzing the frequency domain transformations at certainintervals to determine a value for each of the locations of interestusing a respective one of the time-resolved waveforms, and generatingthe pseudo image comprising pixels, wherein each pixel of the pseudoimage has the value of a respective one of the locations of interest.

The methodologies of embodiments of the disclosure may be particularlywell-suited for use in an electronic device or alternative system.Accordingly, embodiments of the present invention may take the form ofan entirely hardware embodiment or an embodiment combining software andhardware aspects that may all generally be referred to herein as a“processor,” “circuit,” “module” or “system.”

Furthermore, it should be noted that any of the methods described hereincan include an additional step of providing generating a pseudo image ofa device under test (DUT) at a time interval corresponding to anactivation of an element of the DUT. Further, a computer program productcan include a tangible computer-readable recordable storage medium withcode adapted to be executed to carry out one or more method stepsdescribed herein, including the provision of the system with thedistinct software modules.

It should be noted that any of the methods described herein can includean additional step of providing a system comprising distinct softwaremodules embodied on a computer readable storage medium; the modules caninclude, for example, any or all of the appropriate elements depicted inthe block diagrams and/or described herein; by way of example and notlimitation, any one, some or all of the modules/blocks and orsub-modules/sub-blocks described. The method steps can then be carriedout using the distinct software modules and/or sub-modules of thesystem, as described above, executing on one or more hardware processorssuch as 16. Further, a computer program product can include acomputer-readable storage medium with code adapted to be implemented tocarry out one or more method steps described herein, including theprovision of the system with the distinct software modules.

One example of user interface that could be employed in some cases ishypertext markup language (HTML) code served out by a server or thelike, to a browser of a computing device of a user. The HTML is parsedby the browser on the user's computing device to create a graphical userinterface (GUI).

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instructions by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method of generating a pseudo image of a deviceunder test (DUT) comprising: receiving a plurality of locations ofinterest corresponding to locations on the DUT; applying a voltage tothe DUT; acquiring time-resolved photons corresponding to each of theplurality of locations of interest; generating a plurality oftime-resolved waveforms based on the time-resolved photons, each of theplurality of time-resolved waveforms corresponding to a respective oneof the plurality of locations of interest; determining a time-domainwindowing of the plurality of time-resolved waveforms, wherein thetime-domain windowing is determined corresponding to an instance of anexpected switching activity of an element of the DUT at the respectiveone of the plurality of locations of interest; analyzing the pluralityof time-resolved waveforms using the time-domain windowing to determinea value for each of the plurality of locations of interest, wherein eachof the plurality of time-resolved waveforms is integrated at therespective one of the plurality of locations of interest during aplurality of time intervals, indicated by the time-domain windowing,corresponding to the expected switching activity of an element of theDUT, wherein the pseudo image reveals an actual switching activity ateach of the plurality of locations of interest; and generating thepseudo image comprising pixels, wherein each pixel of the pseudo imagehas the value of a respective one of the plurality of locations ofinterest, including the value determined using the new waverformcorresponding to the at least two of the plurality of locations havingthe equivalent signals.
 2. The method of claim 1, wherein generating theplurality of time-resolved waveform corresponding to the respective oneof the plurality of locations of interest comprises aligning a scannerto a location on the DUT corresponding to the respective one of theplurality of locations of interest.
 3. The method of claim 2, whereinthe scanning follows a raster scanning.
 4. The method of claim 1,wherein the plurality of locations of interest are received from acomputer system.
 5. The method of claim 4, wherein the computer systemidentifies the plurality of locations of interest during a priorscanning.
 6. The method of claim 1, wherein the value is displayed as aspecific intensity in the pseudo image.
 7. The method of claim 1,wherein the value is displayed as a specific color in the pseudo image.8. The method of claim 1, wherein the time-domain windowing isdetermined to corresponding to time intervals where no switchingactivity is expected.
 9. A non-transitory computer readable storagemedium comprising computer executable instructions which when executedby a computer cause the computer to perform a method of generating apseudo image of a device under test (DUT), the method comprising:receiving a plurality of locations of interest corresponding tolocations on the DUT; applying a voltage to the DUT; acquiringtime-resolved photons corresponding to each of the plurality oflocations of interest; generating a plurality of time-resolved waveformsbased on the time-resolved photons, each of the plurality oftime-resolved waveforms corresponding to a respective one of theplurality of locations of interest; determining a time-domain windowingof the plurality of time-resolved waveforms, wherein the time-domainwindowing is determined corresponding to an instance of an expectedswitching activity of an element of the DUT at the respective one of theplurality of locations of interest; analyzing the plurality oftime-resolved waveforms using the time-domain windowing to determine avalue for each of the plurality of locations of interest, wherein eachof the plurality of time-resolved waveforms is integrated at therespective one of the plurality of locations of interest during aplurality of time intervals, indicated by the time-domain windowing,corresponding to the expected switching activity of an element of theDUT, wherein the pseudo image reveals an actual switching activity ateach of the plurality of locations of interest; and generating thepseudo image comprising pixels, wherein each pixel of the pseudo imagehas the value of a respective one of the plurality of locations ofinterest, including the value determined using the new waverformcorresponding to the at least two of the plurality of locations havingthe equivalent signals.
 10. The non-transitory computer readable storagemedium of claim 9, wherein generating the plurality of time-resolvedwaveform corresponding to the respective one of the plurality oflocations of interest comprises aligning a scanner to a location on theDUT corresponding to the respective one of the plurality of locations ofinterest.
 11. The non-transitory computer readable storage medium ofclaim 10, wherein the scanning follows a raster scanning.
 12. Thenon-transitory computer readable storage medium of claim 9, wherein theplurality of locations of interest are received from a computer system.13. The non-transitory computer readable storage medium of claim 9,wherein the value is displayed as one of a specific intensity in thepseudo image and a specific color in the pseudo image.
 14. Thenon-transitory computer readable storage medium of claim 9, wherein thetime-domain windowing is determined to corresponding to time intervalswhere no switching activity is expected.
 15. A method of generating apseudo image of a device under test (DUT) comprising: receiving aplurality of locations of interest corresponding to locations on theDUT; applying a voltage to the DUT; acquiring time-resolved photonscorresponding to each of the plurality of locations of interest;generating a plurality of time-resolved waveforms based on an arrivaltime of each of the time-resolved photons, each of the plurality oftime-resolved waveforms corresponding to a respective one of theplurality of locations of interest; analyzing the plurality oftime-resolved waveforms to determine a value for each of the pluralityof locations of interest using a respective one of the plurality oftime-resolved waveforms; and generating the pseudo image comprisingpixels, wherein each pixel of the pseudo image has the value of arespective one of the plurality of locations of interest.
 16. The methodof claim 15, wherein generating the plurality of time-resolved waveformcorresponding to the respective one of the plurality of locations ofinterest comprises aligning a scanner to a location on the DUTcorresponding to the respective one of the plurality of locations ofinterest.
 17. The method of claim 15, wherein the value is displayed asone of a specific intensity in the pseudo image and a specific color inthe pseudo image.
 18. The method of claim 15, wherein each of theplurality of time-resolved waveforms is integrated at the respective oneof the plurality of locations of interest during the time interval,indicated by the time domain representation, corresponding to switchingactivity of an element of the DUT, wherein the pseudo image reveals theswitching activity at each of the plurality of locations of interest.